1. Field of the Invention
The present invention relates to a slotted waveguide antenna and more particularly to a slotted waveguide antenna which is suitable for communications with a communication satellite or a broadcasting satellite.
2. Description of the Prior Art
Parabolic antennas have typically been used for transmitting signals to and receiving signals from a communication satellite or a broadcasting satellite. Recently, however, attention has been directed to planar antennas, since planar antennas are more resistive to wind and snow and are easily installed.
Various antenna plane structures for planar antennas have been proposed in association with linearly polarized waves or circularly polarized waves. Planar antennas typically employ a microstrip or a triplate waveguide having a three conductive layer structure for the feed system. One typically known planar antenna has a waveguide array having a plurality of waveguides arranged in the transverse direction. The waveguide has a plurality of radiating slots arranged in the axial direction. As a result, the waveguide array as a whole has a plane antenna surface. One example of this type of planar antenna is disclosed in W. J. GETSINGER, "Elliptically Polarized Leaky-Wave Array", IRE TRANSACTIONS ON ANTENNAS AND PROPAGATION, pp165-172, March, 1962.
FIG. 1 is a perspective view showing an example of a conventional slotted waveguide antenna. Reference numerals 10, 12, 14, 16 and 18 denote radiating metal waveguides having a plurality of slots 20 for radiating electromagnetic waves on the upper planes thereof. Reference numeral 22 denotes a feed waveguide. The radiating waveguides 10, 12, 14, 16 and 18 are closely disposed in an array form in a manner that their radiating surfaces are on the upper side of the antenna. The feed waveguide 22 is secured to the lower side of the array composed of the waveguides 10, 12, 14, 16 and 18. The feed waveguide 22 has slots for electromagnetic wave coupling in portions where the feed waveguide 22 contacts the respective waveguides 10, 12, 14, 16 and 18.
When this conventional slotted waveguide antenna is manufactured, the respective waveguides 10, 12, 14, 16 and 18 are first made by combining metal plates with a proper precision suitable for a desired frequency, and then the waveguides are secured to each other in a transverse direction in an array-like manner. Subsequently, the feed waveguide 22 is secured to the lower side of the waveguide array. This manufacturing method is not suitable for mass production and thus a slotted waveguide antenna cannot be provided inexpensively using such method. Moreover, this antenna requires reinforcing members to avoid transformation or movement of the waveguides within the waveguide array. The antenna has a three-dimensional structure in which the feed waveguide 22 located on the bottom side of the radiating waveguides. Thus, this antenna loses an advantage of being planar and accordingly the manufacture of the antenna is not easy. The conventional slotted waveguide antenna is therefore not suitable for efficient and cost effective mass production.